1. Field of the Invention
This invention relates to pneumatic tires for use in heavy vehicles such as truck, bus and the like, and more particularly to pneumatic radial tires of this type having a tread of a cap and base structure.
2. Related Art Statement
In the tread reinforced with a belt as in the radial tire, a so-called cap and base structure is often used in order to enhance the durability of the belt. In this connection, rubber having an excellent resistance to heat build-up is used as the base rubber, which exhibits an effect on the durability of the belt and contributes to reduce fuel consumption through the reduction of the rolling resistance of tire.
Even without the necessity of listing references, there has hitherto been well-known the cap and base structure in the tire tread, wherein rubber having an excellent resistance to head build-up serves as a base rubber together with a cap rubber to increase the durability of the belt.
However, when the cap and base structure is applied to a tread of a lug type pattern suitable for running on a poor surface, it becomes apparent that a sufficient effect for preventing separation failure at belt ends beneath the lug is not necessarily obtained. Also, since the base rubber is generally weak to cutting and the growth of cut crack is generally fast in the base rubber, cut failure in the tread center, primarily subjected to cuts in the above application, is counted as one of the defects of the cap and base structure.